As an example of optical transmission technologies, technologies described in Japanese Laid-Open Patent Publication No. 2006-186406 and International Publication Pamphlet No. WO2008/114438 are known. For example, one of the optical transmission technologies is an optical cross-connect device using an MEMS mirror to switch optical paths.
The optical cross-connect device superimposes a control modulation signal of a predetermined frequency (stabilizing control frequency) on a drive signal of the MEMS mirror and performs optimizing control (feedback control) of a mirror angle of the MEMS mirror based on an optical output fluctuation component resulting from the superimposition. In addition, suppression of optical output fluctuation is under study to be able to reduce an impact on other devices of the optical output fluctuation accompanying superimposition of a control modulation signal.
In addition, one of the optical transmission technologies is a technology which superimposes a supervisory signal on main signal light. For example, a supervisory signal may be superimposed on main signal light through intensity modulation of the main signal light with a low frequency.
The conventional technology does not go beyond the study of suppression of the optical output fluctuation component when a modulation signal having a uniform frequency such as the afore-mentioned stabilizing control frequency is superimposed on a mirror drive signal. Stated differently, suppression of the optical output fluctuation component due to an irregular modulation signal which does not having the uniform frequency is not studied. Accordingly, this may lead to deterioration of the transmission quality.